METHOD FOR IMPROVING THE SEPARATION EFFICIENCY OF A CYCLONE SEPARATOR INTENDED FOR GASEOUS FLUID FLOWS

Abstract: The invention concerns a method for improving the separation efficiency of a cyclone separator (10) intended for gaseous medium flows (A). In the cyclone separator (10), the gaseous medium flow (A) to be cleansed flows into the cyclone separator (10) through an inlet duct (12) and ends up in a revolving flow movement (a) inside the cyclone separator (10), which movement is changed, in the bottom end of the conical lower part (14) of the cyclone separator (10), into a revolving tornado flow (b) that flows in the opposite direction. From the incoming medium flow (A), a component flow (c) is taken, which is passed through a component-flow pipe (16), which pipe passes through the centre pipe (13) of the cyclone separator (10), against the tornado flow (b) that has been formed, whereby the component flow (c) disintegrates the tornado flow (b) and thereby prevents solid matter from being carried along with the tornado flow (b), through the centre pipe (13), into the outlet flow (C) of the cleansed medium flow.

Description: Method for improving the separation efficiency of a cyclone separator intended for gaseous fluid flows . The invention concerns a method for improving the separation efficiency of a cyclone separator intended for gaseous medium flows, in which cyclone separator the gaseous medium flow to be cleansed flows into the cyclone separator through an inlet duct and ends up in a revolving flow movement inside the cyclone separator, which movement is changed, in the bottom end of the conical lower part of the cyclone separator, into a revolving tornado flow that flows in the opposite direction. In the prior art, cyclone separators are used for separation of particles of solid matter present in gas flows. In a cyclone separator, the gaseous medium flow enters inside the cyclone separator into a centrifugal flow which revolves inside the cyclone, as a rule, flowing from the top towards the bottom. When the cyclone operates in the vertical position, the inlet of the gaseous medium flow is placed at the top edge of the cyclone separator, in which case the gaseous medium flow that flows in starts revolving downwards inside the cylindrical cyclone separator. When the revolving medium flow flows down into the conical bottom portion of the cyclone separator while maintaining its flow velocity, the revolving medium flow is accelerated at a certain angular velocity. When the revolving medium flow reaches the bottom of the conical bottom portion of the cyclone separator, the revolving medium flow is forced to turn upwards while maintaining its sense of rotation. Then, as is well known, at the lowest point in the bottom end of the cyclone separator, a so-called tornado effect is produced, which is seen, for example, in summer in wind whirls. Frequently, dust and other solid matter is absorbed into such tornado whirls, being carried along by the tornado whirl and raised even to a high altitude. It is only after disintegration of the tornado whirl that the solid matter can fall down freely and be separated from the tornado to the environment. In principle, the same also takes place in a cyclone separator regarding the tornado formed inside the conical part at the lower end. The tornado vortex always carries along with it some of the dust or particles of solid matter entering into the cyclone along with the gaseous medium flow. This is why cyclone separators can, as a rule, not be considered to be very good dust separators, because, along with the tornado flow, even large dust particles can flow out of a cyclone separator, for which reason, by means of the prior-art cyclone separators, a particularly precise separation limit cannot be achieved. At present, a number of different cyclone solutions are used, of which so-called low- pressure, medium-pressure, and high-pressure cyclones should be mentioned. This refers to the pressure loss in the gaseous medium flowing in the cyclone separator that is required by the flowing-through with a nominal volume. Low-pressure cyclones usually have rather large diameters. On the other hand, the diameters of high-pressure cyclones are relatively small. In high-pressure cyclones, the pressure loss may be up to 2000 Pa, whereas in low-pressure cyclones the pressure loss is usually less than 1000 Pa. High-pressure cyclones are often constructed side by side as groups, in which case such a solution is called a multi-cyclone battery. Such a multi-cyclone battery is relatively difficult to manufacture, because it comprises a number of small cyclones, whose dimensional accuracy must be very high. This is why the manufacture of multi-cyclone batteries is relatively expensive. Also, owing to the magnitude of the pressure loss, their operation requires considerably more energy than the operation of low-pressure cyclones does. The efficiency of separation of cyclone separators depends on the centrifugal field formed inside the cyclone separator. It is commonly known that the higher the angular velocity of the gaseous medium flow, the more intensive is the centrifugal field, and that the intensity of the centrifugal field is directly proportional to the second power of the angular velocity of the medium flow. This is why small- diameter cyclone separators are more efficient separators than cyclone separators of larger diameter. It also comes from this that, in practical solutions, multi-cyclones are adopted more and more frequently even though their investment cost and power consumption are higher. In spite of this, cyclone separators are not capable of meeting the requirements of good efficiency of separation. From the prior art, a solution is known by whose means the tornado effect can be eliminated to a reasonable extent. This solution consists of a tornado elimination plate placed at a suitable distance from the orifice of the centre pipe of the cyclone separator, which plate prevents direct flow of the tornado flow into the centre pipe. A drawback of this prior-art solution is intensive wear of the elimination plate, and further, the size of the elimination plate may produce undue wear of the cylinder part of the cyclone separator. The object of the present invention to provide an improvement over the prior-art solutions of cyclone separators. It is a more specific object of the invention to provide a method that permits a considerable improvement of the separation effi- ciency of a cyclone separator. The method in accordance with the invention is characterized in that, from the incoming medium flow, a component flow is taken, which is passed through a component-flow pipe, which pipe passes through the centre pipe of the cyclone separator, against the tornado flow that has been formed, whereby the component flow disintegrates the tornado flow and thereby prevents solid matter from being carried along with the tornado flow, through the centre pipe, into the outlet flow of the cleansed medium flow. Owing to the solution of the present invention, it is possible to eliminate the access of the contents of dust or solid matter contained in a tornado flow into the centre pipe of a cyclone separator and from there further to the outlet flow. By means of the method in accordance with the invention, with a large-diameter cyclone separ¬ ator, a degree of separation is achieved which equals or even exceeds the efficiency of separation of multi-cyclones, but, nevertheless, the gas flow flowing through the cyclone separator does not have to form a pressure loss in excess of 1000 Pa. The invention is based on the idea that the tornado that has been formed in the conical part of the cyclone separator is disintegrated by means of a component flow that flows against the tornado, which component flow is preferably taken, or which is absorbed by itself, from the intake flow of the cyclone separator. Then, the detrimental tornado flow is recirculated among the incoming gaseous medium flow to be cleansed. The component flow is passed preferably by means of a component- flow pipe which passes through the centre pipe of the cyclone and which is substan¬ tially smaller than the diameter of the centre pipe. The absorption of the component flow into this component-flow pipe arises from the differences in pressure present in the cyclone separator, the formation of vacuum arising from the high-velocity movement of rotation of the tornado flow present in the conical bottom portion of the cyclone separator. Owing to the solution in accordance with the invention, the solid matter present in the tornado flow is recirculated to separation, and thereby the overall capacity of separation of the cyclone separator is improved considerably, being equal to the overall capacity of separation of multi-cyclones. The invention will be described in detail with reference to the solution of principle of the invention illustrated in the figure in the accompanying drawing, the invention being, however, not supposed to be confined to said solution alone. The figure in the drawing is a schematic sectional view of a preferred embodiment of a cyclone separator that is used in the method in accordance with the invention. The cyclone separator that is shown in the figure in the drawing is denoted generally with the reference numeral 10. The cyclone separator 10 comprises a frame part, i.e. a cylindrical mantle part 11, an inlet flow duct 12 for the gaseous medium flow A to be cleansed, and a centre pipe 13, through which the cleansed gaseous medium flow flows out as the flow C. The frame part 11 of the cyclone separator 10 is conical at its bottom portion 14. At the bottom of the conical bottom portion 14, there is an outlet opening, which is provided with a closing device 15, through which the solid matter is removed as the flow B. Such a solution is conventional and known from the prior art, and constitutes no part of the present invention as yet. The incoming medium flow A starts revolving inside the cylindrical mantle 11 of the cyclone separator 10 as the flow a, whose direction, as it revolves around the centre pipe 13, is downwards. When the revolving flow a reaches the conical bottom portion 14 of the cyclone separator 10, the flow a starts revolving with an ever shorter radius of rotation, while the flow a, nevertheless, still corresponds to the velocity of the incoming flow A. This is why, in the conical bottom portion 14, the angular velocity of the flow a becomes ever higher and higher. Then, the centrifugal force/field increases in proportion to the second power of the angular velocity, and this is why, in the increasing centrifugal field, the particles of solid matter are cast onto the walls of the comcal lower portion 14, from where they sink into the outlet opening of the conical bottom portion 14 and through said opening into the closing part 15 in itself known, from which they can be removed as the flow B. At the lower end of the conical bottom portion 14, the flow a is converted to a flow b that is directed upwards, i.e. to a so-called tornado flow, which has the same sense of rotation as that of the flow a, but whose direction is towards the lower orifice of the centre pipe 13. The tornado flow b penetrates into the interior of the flow a of opposite principal flow direction, because of the conical shape of the conical lower portion 14. As the flow velocity continues to be substantially the same as the flow velocity of the incoming medium flow A, the angular velocity of the tornado flow b becomes multiple as compared with the angular velocity of the flow a. This results in the formation of an intensive vacuum inside the tornado flow b and in its close vicinity. According to the invention, inside the centre pipe 13 of the cyclone separator 10, preferably on the central axis of the centre pipe, the component-flow pipe 16 is placed, whose diameter is considerably smaller than the diameter of the centre pipe 13. The open lower end of the component-flow pipe 16 is directed directly towards the tornado flow b that was formed in the conical bottom portion 14. The compo¬ nent-flow pipe 16 extends preferably beyond the orifice of the centre pipe 13 towards the conical bottom portion 14 in order that the vacuum effect produced by the tornado flow b should become sufficiently intensive to produce the component flow c, preferably out of the medium flow A flowing into the cyclone separator 10. The top end of the component-flow pipe 16 preferably extends to the vicinity of the top end of the centre pipe 13, where it passes through the wall of the centre pipe 13. The component flow c entering from there into the component-flow pipe 16 can disintegrate the tornado flow b and the solid matter contained in same as the component flow c is discharged from the bottom end of the component-flow pipe 16. Thus, the solid matter contained in the tornado flow b is dispersed among the flow a, being thereby recirculated to separation. When the component flow c is taken from the medium flow A entering into the cyclone separator 10, its magnitude in comparison to the medium flow A is negli¬ gible, as a rule, less than 10 per cent by volume, preferably 0.1...5 per cent by volume. Thus, this component flow c takes place entirely by itself inside the cyclone separator 10. Such a component flow c requires a difference in pressure of 200...500 Pa, which is already produced also in low-pressure cyclones when the cyclone receives its nominal flow A. Of course, the flow entering into the component-flow pipe 16 is already partly produced out of the difference in pressure, arising from the pressure loss of the cyclone, present at the orifice of the centre pipe 13 as compared with the pressure present at the inlet opening 12 of the cyclone. Having disintegrated the tornado flow b, the component flow c discharged out of the component-flow pipe 16 enters into the flow a revolving inside the cyclone. By means of the method in accordance with the invention, a very high increase in the efficiency of separation is achieved, as compared with the efficiency of separ¬ ation of a conventional cyclone. By means of the invention, it is possible to eliminate the tornado effect completely, which effect is present in every cyclone when it is in operation. On the other hand, the effect of the solution in accordance with the invention on the construction, cost of manufacture, and on the appearance of the cyclone separator remains fully negligible. The location of the lower end of the component-flow pipe 16 in the conical bottom portion 14 depends, among other things, on the steepness of the conical lower portion 14 and on the velocity of the flow a, i.e. on the loading of the cyclone. Generally speaking, the initial end of the conical lower portion 14 can be considered to be a preferable location of the lower end of the component-flow pipe 16, but the invention is by no means critical in respect of the precise location of the lower end of the component-flow pipe 16. It is the principal objective of the invention that the component flow c entering into the component-flow pipe 16 should be, as precisely as possible, equal to the amount that is required for complete disintegration of the tornado flow b formed in the cyclone separator 10. This must, of course, be found out and measured for each cyclone construction separately. Owing to the invention, the medium flow cleansed by the cyclone separator 10 can be made to escape into the centre pipe 13 as cleansed from the solid matter contained in the tornado flow b. In such a case, the cleansed medium flow C departing from the centre pipe 13 of the cyclone 10 is as clean as possible. Above, the solution of principle of the invention has been described only, and it is obvious for a person skilled in the art that numerous modifications can be made to said solution within the scope of the inventive idea defined in the accompanying claims.

Claims: Claims 1. A method for improving the separation efficiency of a cyclone separator (10) intended for gaseous medium flows (A), in which cyclone separator (10) the gaseous medium flow (A) to be cleansed flows into the cyclone separator (10) through an inlet duct (12) and ends up in a revolving flow movement (a) inside the cyclone separator (10), which movement is changed, in the bottom end of the conical lower part (14) of the cyclone separator (10), into a revolving tornado flow (b) that flows in the opposite direction, c ha ra c te r i z e d in that, from the incoming medium flow (A), a component flow (c) is taken, which is passed through a compo¬ nent-flow pipe (16), which pipe passes through the centre pipe (13) of the cyclone separator (10), against the tornado flow (b) that has been formed, whereby the component flow (c) disintegrates the tornado flow (b) and thereby prevents solid matter from being carried along with the tornado flow (b), through the centre pipe (13), into the outlet flow (C) of the cleansed medium flow. 2. A method as claimed in claim 1, characterized in that, as the compo¬ nent flow (c), a flow is used that is less than 10 per cent by volume of the incoming medium flow (A). 3. A method as claimed in claim 2, characterized in that, as the compo¬ nent flow (c), a flow is used that is 0.1...5 per cent by volume of the incoming medium flow (A). 4. A method as claimed in any of the claims lto3, characterized in that the distance of the lower end of the component-flow pipe (16) from the orifice of the centre pipe (13) is regulated in order to bring the vacuum effect produced by the tornado flow (b) to the desired level. 5. A method as claimed in any of the claims lto3, characterized in that the location of the lower end of the component-flow pipe (16) is fitted such that the tornado flow (b) has had time to be formed completely. 6. A method as claimed in any of the claims lto5, characterized in that, as the component-flow pipe (16), a pipe is used whose diameter is considerably smaller than the diameter of the centre pipe (13).

Inventors: JAERVENPAEAE VILJO, JAERVENPAEAE, VILJO
Applicants: JAERVENPAEAE VILJO, WISER OY, JAERVENPAEAE, VILJO
Application year: 1994
Main classification: B04C5
IPC codes: B01D45, B04C5